TAILIEUCHUNG - Báo cáo Y học: Substrate selectivity and sensitivity to inhibition by FK506 and cyclosporin A of calcineurin heterodimers composed of the a or b catalytic subunit

The calcineurin (CaN) a and b catalytic subunit isoforms are coexpressed within almost all cell types. The enzymatic properties of CaN heterodimers comprised of the regulatory B subunit (CnB) with either the a or b catalytic subunit were compared using in vitro phosphatase assays. CaN containing the a isoform (CnAa) has lower Km and higher Vmax values than CaN containing the b isoform (CnAb) toward the PO4RII, PO4-DARPP-32(20–38) peptides, and p-nitrophenylphosphate (pNPP). | Eur. J. Biochem. 269 3540-3548 2002 FEBS 2002 doi Substrate selectivity and sensitivity to inhibition by FK506 and cyclosporin A of calcineurin heterodimers composed of the a or b catalytic subunit Brian A. Perrino1 Andrew J. Wilson2 Patricia Ellison3 and Lucie H. Clapp2 1Department of Physiology Cell Biology University of Nevada School of Medicine Reno NV USA 2Center for Clinical Pharmacology University College London UK 3Department of Biochemistry University of Nevada School of Medicine Reno NV USA The calcineurin CaN a and b catalytic subunit isoforms are coexpressed within almost all cell types. The enzymatic properties of CaN heterodimers comprised of the regulatory B subunit CnB with iti thet the a or b catalytic subunit were compared using in vitro phosphatase assays. CaN containing the a isoform CnAa has lower Km and higher Vmax values than CaN containing the b isoform CnAb toward the PO4-RII PO4-DARPP-32 20-38 peptides and p-nitrophenyl-phosphate pNPP . CaN heterodimers containing the a or b catalytic subunit isoform displayed identical calmodulin dissociation rates. Similar inhibition curves for each CaN heterodimer were obtained with the CaN autoinhibitory peptide CaP and cyclophilin A cyclosporin A CyPA CsA using each peptide substrate at Km concentrations except for a five- to ninefold higher IC50 value measured for CaN containing the b isoform with p-nitrophenylphosphate as substrate. No difference in stimulation of phosphatase activity towardp-nitrophenylphosphate by FKBP12 FK506 was observed. At low concentrations of FKBP12 FK506 CaN containing the a isoform is more sensitive to inhibition than CaN containing the b isoform using the phosphopeptide substrates. Higher concentrations of FKBP12 FK506 are required for maximal inhibition of b CaN using PO4-DARPP-32 20-38 as substrate. The functional differences conferred upon CaN by the a or b catalytic subunit isoforms suggestthatthe a b and CaN substrate ratios may .

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